The present invention relates to a sheet separation apparatus for use in an electrophotographic copying machine.
In an electrophotographic copying machine, it is necessary to separate a transfer sheet from the peripheral surface of a photoconductor drum after a toner image formed on the drum is transferred to the transfer sheet. Referring to FIGS. 1 and 2, there are shown the conventional methods for performing such separation of a transfer sheet from a photoconductor drum 1. Referring to FIG. 1, when a leading edge of a transfer sheet 2 comes close to a separator 3, an operation shaft 4 is lowered and the separator 3 is rotated on a shaft 5 in the direction of the arrow, so that a top portion of the separator 3 is brought into pressure contact with the photoconductor drum 1 and the sheet 2 is separated from the photoconductor drum 1.
The separator 3 as shown in FIG. 2 is urged to rotate clockwise by the bias of a spring whose one end is fixed to a projection 3a of the separator 3 and whose other end is fixed to a pin 6. Normally the separator 3 is held in a position as indicated by long and short dash lines. When the leading edge of the transfer sheet 2 comes close to the separator 3, an operation pin 7 which is rotated together with the drum 1 pushes the projection 3a of the separator 3, and the separator 3 is turned to a position as indicated by solid lines, so that the sheet 2 is separated from the drum 1. In the above-mentioned sheet separation apparatus, a plurality of the separators 3 are secured to the shaft 5, so that the separators 3 are integrally operated. Therefore, the top portions of the separator 3 have to be adjusted so as to be arranged in a line accurately. In case the top portions of the separators 3 are irregularly arranged, the sheet separation cannot be performed properly. Furthermore, since each separator 3 is operated rigidly towards the peripheral surface of the drum 1 by the rotation of the shaft 5, occasionally the operation stroke of the separator 3 becomes too great, and when more than a predetermined load is applied to the end portion of each separator 3, there is a risk that the separators 3 and the peripheral surface of the drum 1 are damaged.
Referring to FIG. 3, there is shown part of a copying machine in which a sheet-formed photoconductor 8 is wound around the peripheral surface of the drum 1. One end portion of the photoconductor 8 is in pressure contact with a concave portion of the drum 1 by a holding member 11 whose base portion is rotatably mounted on a shaft 9. The other end portion of the photoconductor 8 is in pressure contact with the concave portion of the drum 1 by a clamp member 12. In the copying machine of this type, it is necessary to prevent a portion of the photoconductor 8 capable of forming images from being damaged by the separator 3 with the transfer sheet 2 advanced up to a photoconductor clamping portion. In this case, if the top portion of the separator 3 is acute, the separator 3 is pushed towards the shaft 5 as indicated by the arrow when the top portion of the separator 3 is at a slanting surface of the clamping portion, resulting in that the separator 3 is damaged.
Furthermore, in the conventional sheet separation apparatus, a sheet separation unit is secured to the body of the copying machine and plural separators 3 which are made substantially integral are brought into contact with the peripheral surface of the drum 1 or moved away from the drum 1. Therefore, when a sheet is jammed in the sheet separation portion, it is very difficult to remove the jammed sheet and to fix the sheet separation portion. Furthermore, since the separators 3 are fixed to the shaft 5, when an unusual load is applied to the separators 3, the separators 3 are apt to be damaged.
Furthermore, in the copying machine of the type as shown in FIG. 3, when the leading edge of the transfer sheet is curled or charged electrically so as to be in close contact with the clamp member 12, the separator 3 sometimes fails to enter between the sheet 2 and clamp member 12 so that the sheet is jammed.